How the Army uses radios.
As today's battlefield conditions change, military communications are rapidly evolving. Specialized radio systems operate in the spectrum between DC and lightwave. Specific frequencies depend on radio-wave propagation performance.
Let's focus on the high-frequency (HF) and low-band very-high-frequency (LB VHF) bands encompassing the 2- to 90-MHz spectrum. Tremendous performance and price improvements in HF/LB VHF continue to emerge from new technology.
Digital Is Strong
By far the biggest contributor to these new capabilities is the augmentation and replacement of traditional analog circuits by digital circuits. Current HF exciters and receivers have only one traditional analog function: the RF final conversion.
Other functions--audio, modulators/demodulators, synthesizers, IF, and AGC/TGC--can now be accomplished digitally, with significantly better performance in almost every case. This digital revolution encompasses computer and digital-signal processing (DSP) chips, and Application Specific Integrated Circuits (ASICs).
Secondary benefits are lower power consumption, increased packaging density, improved production yields, better temperature-variation performance, and simplified design-parameter modeling.
High-speed modems that permit error-corrected HF 2400-b/s (as compared to traditional 50-b/s) and LB VHF 9.6-kb/s data throughputs are a direct result of revolutionary new digital technology.
Running concurrently is a software-development explosion. Engineering staffs now have as many digital-software engineers as traditional RF analog engineers--if not more. A radio-control system may have over 250,000 lines of code. Networking, with packet-switching techniques, is now extended to tactical radio users. It's not limited to higher echelons.
Traditional component performance is also improving--especially maximum frequency and voltage parameters. This is particularly important for transistors, diodes, capacitors, and component mounting materials. Manufacturers are now able to produce broader-frequency-range radios, higher-power fast-tuning antenna couplers, and improved solid-state broadband power amplifiers.
Meeting Key Criteria
* Information Form: Traditional voice and low-speed data are being augmented with high-speed data, fax, and video. Of these, video yields the greatest increase in performance. Some of the latest digital video-imaging transmission systems let high-resolution color still-frame images be reliably transmitted via any narrowband 3-KHz circuit. Even the most difficult multiple-hop HF skywave path may be used. Integrated with radios in many of these systems are data compression; high-speed modems with forward error correction, interleaving, and adaptive channel equalization; and video-control algorithms. Military users interested in video include special-operations forces and federal agencies fighting the war on drugs.
* Information Security: Information transmitted via radios has traditionally been protected using separate boxes. New technologies now allow substantial reduction in the hardware necessary to perform the security function. These devices can be embedded within the radio, substantially reducing the volume, weight, and power for a user, especially a tactical user. Systems employing crypto devices can include frequency hopping, spread spectrum, low probability of intercept detection, RF power optimization, and burst transmission.
* Acceptable Error Performance: Complex mathematical algorithms are now being implemented with DSP techniques. High-speed closed-loop automatic repeat-request systems are specified when 100% accuracy is mandatory. This results in a more reliable system than those implementing a forward-error-correction algorithm only.
* Mission-Suitability and Physical Characteristics: Newer equipment must be smaller and lighter. It must consume less power and provide tremendously increased performance. As a comparison, it is possible to package an HF radio with high-speed data, automatic link establishment (ALE), 800-Hz LPC voice digitization, encryption, and a frequency-hopping controller--all in a shoebox-size case. A comparable capability in the mid-1980s required a 6-foot rack of equipment. Electromagnetic pulse (EHP) filters are also being incorporated. Operation over multiple-frequency bands, with corresponding modulation modes, is becoming the norm. Thus, radios operate over all or portions of the SSB, LB VHF, high-band VHF and UHF frequency bands.
* Simple Operation: HF equipment interface has been made routine by implementation of ALE. The U.S. government has released a MILSPEC governing this protocol. NATO is working on a comparable STANAG standard. This ALE process performs HF circuit connectivity, making HF operation as routine as other line-of-sight VHF/UHF circuits.
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|Date:||Jan 1, 1991|
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